Electric cables used at present include strength members so that they can be suspended between posts or vertically. These strength members are constituted by steel wires which carry the mechanical stresses. These wires are sometimes inserted in the cores of cables (coaxial sub-marine cables) or between conductors. In most cases they are wound round cables and constitute their outer reinforcement.
The disadvantage of metal strength members is that they modify the dielectric characteristics of the insulation. Further, they increase the volume of the cable when they constitute its outer reinforcement and in any case, they increase its weight very appreciably.
It has already been proposed to provide electric cables with longitudinal strength members made of a synthetic resin, for example an aliphatic polyamide such as Nylon, or ethylene-glycol polyterephthalate or polyesters, or polyolefines, or polycarbonates, etc. (French Pat. No. 2 039 355, U.S. Pat. Nos. 3,265,809 and 3,980,808). Such strength members have the disadvantage of allowing the cable to elongate appreciably and of not being very resistant to moisture, so that metal strength members have continued to be used despite their disadvantages.